Various synthetic roof and wall coverings are known today, such as those formed of elongated thermoplastic panels that are nailed to the wall or roof support surface in horizontal courses or rows in partially overlapping relation to each other so as to provide a substantially water resistant, protective layer over the support surface. While it is desirable that the panels facilitate drainage of rain water and the like to which they are exposed in the outside environment, heretofore this has presented problems. Because of the surface tension of water, capillary action often causes water to be drawn inwardly between overlapping marginal edge portions of adjacent panels and enter the space beneath the panels, either through nail holes or about the peripheral edges of the panels, becoming trapped under the panels. Such capillary water movement worsens during high wind and storm conditions. Not only does the trapped moisture under the panels increase the possibility for leakage and damage to the wall or roof, but upon freezing, the expanding moisture tends to lift the overlapping edge portions, further breaking the protective barrier between the panels and the support surface.
The above identified Crick et al. applications Ser. Nos. 07/487,910 and 07/488,351, disclose synthetic wall and roof panels formed with water barrier ridges that impede capillary movement of water between overlapping marginal edge portions of adjacent panels and facilitate drainage. Since such panels are made of plastic and are relatively large in size, typically having a length of 48 inches or more, the panels tend to easily bend and deform upon handling and upon mounting on even slightly irregular wall and roof surfaces, which often occurs when the panels are being used as a replacement covering on an existing wall or roof. Deformation and bending of the panels, either as a result of mounting or because of exposure to severe weather conditions, can destroy peripheral seals between panels and permit leakage onto the support surface, notwithstanding the water barrier and drainage ridges.